The invention generally relates to the area of telephonic data transmission facilities. More particularly, the present invention concerns methods and apparatuses for improving the signal quality, and thus data rate, of telephonic links between service provider modems and subscriber client modems.
The V.90 (56 Kbps) modem protocol was introduced with much fanfare by manufactures, and Internet users rushed out to get their hands on the answer to their frustrations arising from slow downloads of information from the Internet via Internet service providers (ISPs). Before, the V.90 protocol was introduced, the highest speed for such data transfers was 33.6 Kbps via V.34 protocol modems. The V.90 modems are theoretically capable of receiving data from a sender at about a 50% faster rate. However, theory and reality are two very different concepts. This has certainly been the case with V.90 modems.
As many disappointed users of 56 Kbps modems discovered, having the fastest telephone-based client modem on the Internet does not mean that the user""s computer will receive information from an Internet service provider at the highest theoretically available data rate. The best client modems on the market today are theoretically capable of receiving data from ISPs using the V.90 protocol at a rate of over 50 Kbps and sending data using the V.34 protocol at a rate of over 33 Kbps. However, when a user of these state-of-the-art modems attempts to remotely connect to an ISP server advertised to support V.90 connections, the user""s lofty expectations of high speed transmissions are brought down to earth when the user receives notification from the computer that the connection was established (negotiated) at a lower speed than the expected rate of over 50 Kbps. For example, rather than 50 Kbps, the user""s modem connects at a receive rate less than 40 Kbps, a speed much closer to the 33.6 Kbps of last year""s clearance shelf modems.
Who is responsible for the owners of V.90 client modems inability to connect to an ISP V.90 server modem at the maximum bit rate? It""s not the ISP""s fault. The V.90 ISP modems today are indeed capable of transmitting at the maximum rate under the V.90 protocolxe2x80x94about 50 Kbps. Manufacturers of V.90 modems are not to blame either. The modem is indeed capable, under favorable conditions, to accurately receive data in accordance with the V.90 protocol at an effective transfer rate of over 50 Kbps.
In actuality no one is wholly responsible for V.90 modems present performance shortcomings in the real world. The problem arises from the fact that developers of the V.90 protocol pushed the capabilities of twisted pair copper wire, the primary means for transmitting telephone signals from central offices to end-users, to its limit. Having done so, the V.90 protocol works in a noise-free laboratory environment and under certain, limited, uses outside the laboratoryxe2x80x94such as when a user is within shouting distance of the central office (CO) of its telephone service provider. This is not a likely scenario for most users of V.90 client modems. In fact, the problem of less than ideal telephone signal transmission media creates problems for Internet subscribers at even lower transmission speeds using the older V.34 protocol having greater noise margins.
The source of the problem is the marketplace""s unquenchable thirst for high speed data transmission. Both the providers and the receivers of information want data transmissions to occur at substantially higher rates than the transmission rates when the telephone companies laid their massive networks of local subscriber lines. However, the high performance transmitters and receivers cannot make up for a transmission media that simply cannot satisfactorily transmit the information at such a high rate, over the required distances, under real world circumstancesxe2x80x94including noise, interference, and power limitations. The solution rests in the hands of the parties responsible for transmitting the signals from the ISPs to the usersxe2x80x94the phone companies. To that end, the phone companies could scrap the old twisted wire for optic fiber and coaxial cable. Such solutions are extremely costly and require overhauling the twisted wire network laid down by phone companies over several decades. As a result, achieving the maximum data transmission rates using V.90 modems is not a likely event for many, if not most, typical phone service customers.
Today, xe2x80x9cpair gainxe2x80x9d technology provides enhanced digital data transmission over twisted pair copper lines between central offices (COs) and end-users. Pair gain technology uses the pre-existing twisted pair copper wire technology and transmission media. However, pair gain systems apply their own set of data transmission protocols, including A/D and D/A conversion at the central office and end-user connections, respectively. An advantage of pair gain systems provided to phone companies is the ability of phone companies to add phone lines without increasing the number of twisted pair wires for a given area served by a single twisted pair. A single twisted pair line can be transformed from handling a single phone line to one handling two or more phone lines.
Another advantage of pair gain systems is that they provide enhanced signal transmission quality over the twisted wire media. In particular, known pair gain systems are capable of transmitting digitized data over longer distances, and with fewer errors than standard analog transmissions over the same twisted pair transmission media. One such provider of pair gain systems is Charles Industries, Ltd., 5600 Apollo Drive, Rolling Meadows, Ill.
However, even pair gain systems cannot overcome some shortcomings of twisted wire phone networks that were initially intended to convey, using an analog signal, a recognizable voice rather than errorless digital information. As a result, by the time data signal from a V.90 ISP modem reaches the central office terminal of a pair gain system, the signal has been degraded by passes through one or more analog telephone switches. The central office terminal of the pair gain system converts the analog signal from the central office switch to a digital signal. The remote terminal (at the telephone subscriber""s location) converts the digital signal from the central office terminal back to the analog signal transmitted by the central office switch. Inserting the A/D and D/A conversion by the pair gain system into the transmission path between the ISP and the telephone service subscriber causes a signal loss that prevents successful transmission of data between ISPs and users at the maximum available rate under the V.90 protocol.
The present invention improves the quality and accuracy of data transmissions in order to overcome some, if not all, of the problems encountered when attempting to realize the advertised capabilities of the present state-of-the-art voice band modems. The method and apparatus of the present invention seeks to provide a high precision, reliable, and economically practical high-speed link between server modems and subscriber client modems connected by a path that includes at least one analog transmission link.
In accordance with the present invention, a first encoded analog data signal is transmitted over analog transmission media, such as twisted pair wire. The first encoded analog data signal corresponds to an original data set to be transmitted from a service provider modem to a subscriber client modem. A demodulator, such as the type found in client-type modems, receives the encoded analog data signal and recovers the encoded digital data from the analog signal. Digital data corresponding to the recovered digital data is again encoded to render a second encoded analog data signal substantially the same as the first encoded analog data signal. The second encoded analog data signal is received by a subscriber client modem.
In accordance with another aspect of the present invention, a server-type modem encodes digital data rendered from the first recovered digital data set. In a particular claimed embodiment of the present invention, the server-type modem is located at the central office terminal. In that case, the server-type encoding functions are performed on data arising from the first recovered digital data set before the data is transmitted from a central office terminal to a remote terminal of a digital link (e.g., a pair gain system). In another particular claimed embodiment of the present invention, the server-type modem is located at the remote terminal. In that case, the server-type encoding functions are performed after the digital data has been transmitted from the central office terminal to the remote terminal of the digital link.